The invention relates generally to water-cooled members for supporting steel slabs and the like in reheating furnaces, and, more particularly, to refractory insulation for such members.
In the processing of steel, ingots are rolled into shapes such as slabs and subsequently reheated in furnaces for further rolling or other processing. Reheat furnaces are typically pusher furnaces, walking beam furnaces or a combination of the two. Each features a series of lengthwise supports, frequently called skid pipes or skids. These skids are supported in an elevated state by vertical supports so that both sides of the steel slabs may be heated as they travel through the furnace. The steel slabs are typically 9 to 10 inches thick, 30 to 82 inches wide and 30 to 40 feet long and are heated to final temperatures of 2100.degree. F. to 2500.degree. F., depending upon the type of steel and its intended use.
In pusher furnaces, the steel slabs are abutted front-to-back and slide along The skids as they are pushed through the furnace. As a fresh steel slab is introduced into the input end of the pusher furnace, a corresponding heated steel slab is extracted from the discharge end for rolling mill treatments or other processing. In contrast, a typical walking beam furnace has a number of fixed skids with "walking skids" positioned between them. The walking skids are equipped to rise upward, advance forward, withdraw downward and return to their original positions so that the steel slabs within the furnace are incrementally moved forward. In both pusher and walking beam furnaces, the top surfaces of the skids are equipped with wear castings, also known as "riders", that support the steel slabs.
The skids and vertical supports in reheat furnaces must be compact in order to leave sufficient combustion space in the furnace chamber, must be strong enough to support the heavy steel slabs being treated and must be protected against injury by the high temperatures. As a result, hollow metal pipes through which cooling water is circulated are typically used in the construction of these components. If water-cooled pipes with bare outer surfaces are used for the skids and vertical supports, however, the absorption of heat through the pipe metal to the cooling water results in tremendous heat loss from the furnace. It is therefore necessary to insulate the pipes to minimize the heat loss.
Covering the pipes with insulation also protects them from damage due to the high temperature of the furnace.
Previous insulation systems have utilized preformed refractory members that are welded directly to the pipe. Examples of this type of insulation system may be found in U.S. Pat. Nos. 3,647,194; 3,804,585; 4,070,151; 4,134,721 and 4,528,672. These insulation systems utilize members constructed of refractory material within which metal links, coils or fasteners are embedded. A portion of the metal link, coil or fastener is left exposed through a hole in the refractory material. Alternatively, the metal link, coil or fastener may extend out of an end of the member. The refractory members are sized so that they fit upon the pipe being protected. Once positioned on the pipe, the exposed portion of the metal link, coil or fastener may be welded directly to the surface of the pipe.
While these insulation systems have proven effective, the movement of the heavy steel slabs during the heating process causes the skids to flex and vibrate. The impacts of the slabs also subject the skids to shocks. The flexing, vibration and shocks, along with the cyclical heating of the furnace to extremely high temperatures, results in occasional damage to the refractory members necessitating their replacement. Replacement of the refractory members requires that the welds be broken and the remaining weld material ground off the pipe surface. This is a time consuming and labor intensive process during which the furnace may not be operated. Furnace downtime adversely affects the profitability of the operation and must be minimized.
An alternative type of insulation system utilizes preformed refractory members that fasten together to cover pipes. Examples of these types of systems may be found in U.S. Pat. Nos. 3,781,167; 4,182,609; 4,225,307; 4,312,385; 4,424,028 and 4,505,303. In each of these systems, the refractory members are cast so as to include fastening devices such as tabs, clips or hooks. The fastening devices join neighboring, refractory members together after they are positioned upon the pipe. While these systems have also proven to be effective, the replacement of a single refractory member requires that neighboring members also be removed, or at least shifted. This is because each refractory member depends upon neighboring refractory members for support. This complicates the replacement process so that the furnace downtime increases. In addition, there is a greater chance of damage to neighboring refractory members.
U.S. Pat. Nos. 3,941,160 and 4,228,826 disclose interlocking, refractory members for covering and insulating pipes. More specifically, the refractory members are shaped so that they slide into engagement with one another as they are positioned on a pipe. A disadvantage of this arrangement is that, due to abutting neighbor members, a damaged member must be cut in order to be removed. This increases the complexity and time of the replacement process.
A further disadvantage of many of the above insulation systems is that, by utilizing refractory members that are abutting or that are attached by their ends to the pipe, they do not allow for thermal expansion of the refractory members. More specifically, when heated to the extreme temperatures of a reheat furnace, the refractory members may expand against each other or the weld so that they crack.
Finally, U.S. Pat. No. 3,820,947 discloses a fibrous ceramic insulating blanket that is wrapped about a pipe and pressed over anchor studs that project from the pipe. A ceramic anchor is placed over each stud and secured by a nut so that the blanket is held in position against the pipe. The assembly is sprayed with a liquid which hardens to provide a relatively hard and erosion-resistant outer-layer over a resilient inner-layer. A disadvantage of this construction is that it is difficult to replace a single section of the insulation even though only a small portion may be damaged.
Accordingly, it is an object of the present invention to provide a pipe refractory insulation system wherein the refractory members may be quickly replaced.
It is another object of the present invention to provide a pipe refractory insulation system wherein the refractory members may be replaced without removing welds from the pipe.
It is another object of the present invention to provide a pipe refractory insulation system wherein a refractory member may be replaced without disturbing additional refractory members.
It is another object of the present invention to provide a pipe refractory insulation system wherein a refractory member may be replaced without being cut for removal.
It is still another object of the present invention to provide a pipe refractory insulation system that accounts for thermal expansion of the refractory material.
It is still another object of the present invention to provide a pipe refractory insulation system wherein a single section of the refractory material may be replaced.